[The Kyoto Protocol] is either too much or too little. It is too much if, as most scientists believe, global warming will continue to be a gradual process, producing really serious effects...only toward the end of the century. For by that time science, without prodding by governments, is likely to have developed economical “clean” substitutes for fossil fuels (we already have a clean substitute—nuclear power) and even economic technology for either preventing carbon dioxide from being emitted into the atmosphere by the burning of fossil fuels or for removing it from the atmosphere. But the Protocol, at least without the participation of the United States, is too limited a response to global warming if the focus is changed from gradual to abrupt global warming.
This is an important point. The present value of a reduction in environmental damage in the year 2099 is quite low. To pay a huge price now in order to achieve such a reduction is not sound. See Lomborg's Lessons.
When climatologists construct models of global warming caused by industrial emissions of CO2 and other greenhouse gases, they are much more like economists than the typical experimental biologist or physicist. By that I mean that they can only test the implications of their models with the data thrown up by current and past actual events, not by experimental isolation of particular forces.
To me, climate models are like macroeconometric models. Those models, which are used to analyze and forecast unemployment, inflation, and so on, are certainly not one of the economics profession's shining successes.
One of the reasons that the climate models show that the required reduction in emissions is so large is that the coefficient on emissions is so small. That is, the response of temperature change to emissions is relatively small, so that in order to reduce global temperatures, we have to make dramatic cutbacks in emissions--and then pray that the models are indeed correct.
Posner argues that it is abrupt climate change that ought to concern us. What I would say in response is that if climate change is going to come abruptly, then the major climate models are wrong. Therefore, before we adopt a policy to deal with abrupt climate change, we would need to come up with new climate models that predict such change, presumably with some basis in reality. Then, we would have to re-examine the emissions targets of Kyoto in light of these new climate models. But to take an emissions target derived from models of slow climate change to address a fear of rapid climate change strikes me as taking a stab in the dark.
For Discussion. Are there some reputable climate models that do predict abrupt climate change?